Chord axial compressive behavior of hybrid FRP-concrete-steel double-skin tubular member T-joints

Abstract

Hybrid fiber reinforced polymer (FRP)-concrete-steel double-skin tubular members (DSTMs) are a promising form of structural members with superior mechanical performance and durability, which have great potential for application in ocean structures. Such hybrid DSTMs consist of three components: an inner steel tube, an outer FRP tube, and concrete filled between the two tubes. Despite a significant number of studies demonstrating the excellent performance of hybrid DSTMs, no studies have been concerned with the joints of these members. The lack of a reliable design method for DSTM joints is certainly a huge obstacle to their wide application in practice. Against the above background, a research project has been proposed to understand the static behavior of circular DSTM T-joints through a combined experimental, modeling, and theoretical study. This paper presents the results of an experimental program on the axial compressive behavior of the chord in DSTM T-joints. The effects of various important factors, such as FRP tube thickness, steel tube thickness, brace-to-chord diameter ratio, void ratio, and concrete strength, on the performance of the DSTM T-joints were examined in detail. The test results demonstrated that the DSTM T-joints exhibited a ductile behavior provided that the joint region was appropriately strengthened and the presence of a brace did not significantly affect the compressive behavior of the chord in the joints with a brace-to-chord diameter ratio of 0.5. Finally, a simple method was proposed to predict the axial load-axial strain behavior of the DSTM T-joints.